Improved textile materials and methods and apparatus for preparing the same



Jan. 5, 1960 E. D. BOLINGER ETAL 2,919,534 IMPROVED TEXTILE MATERIALSAND METHODS AND APPARATUS FOR PREPARING THE SAME Filed Nov. 2 1955 2Sheets-Sheet 1 IIII INVENTORS E. DARE BOLI NGER By NORMAN E. KLEINATTORN EY Jan. 5, 1960 E. D. BOLINGER ETAL 2,919,534

IMPROVED TEXTILE MATERIALS AND METHODS AND APPARATUS FOR PREPARING THESAME Filed Nov. 2, 1955 2 Sheets-Sheet 2 INVENTORS EDGAR DARE BOLI NGERNORMAN E. K LEIN ATTOR NEY United States Patent IlVIPROVED TEXTILEMATERIALS AND METHODS AND APPARATUS FOR PREPARING THE SAME Edgar DareBolinger, Clemson, and Norman E. Klein,

1 Pendleton, S.C., assignors to Bearing Milliken Research Corporation,near Pendleton, S.C., a corporation of Delaware Application November 2,1955, Serial No. 544,521

29 Claims. or. 57-34 March 1, 1952.

It is well known in the art that fabrics woven of yarns which tend tocrinkle or curl in an untensioned state have an elastic nature and suchfabrics are widely employed for the manufacture of wearing apparel togive a better fit to the consumer and to enable a single size of articleto be employed to accommodate a large range of appendage or body sizes.For example, elasticized nylon fabrics are widely employed in themanufacture of hosiery and only two or three sizes of hose need bemanufactured since this small number is sufiicient to accommodate allnormal leg and foot sizes. Likewise, elasticized fabrics are employed inthe manufacture of sweaters and undergarments, in the manufacture ofbeddings and in the manufacture of childrens socks. In the latterinstance, the elasticized articles have the additional advantage thatthey can be worn for a period of years without being outgrown.

A number of processes have been suggested for the production of yarnsfor use in the preparation of elasticized fabrics. According to oneprocess, it is proposed that continuous filament yarns be highlytwisted, heatset while in a highly twisted condition and untwisted topro- .duce an elasticized .yarn. According to another prior art methodit is suggested that a yarn forming material be extruded betweenintermeshing gears or the like so that the filaments solidify with acrinkled configuration. It has likewise been proposed that filaments bepassed between interrneshing gears or crimping wheels in the presence ofheat or softening agents in an effort to obtain a permanent crimptherein, and it has been further suggested that a continuous filament bedrawn at room temperature over. a dull knife edge or other deformingtool in an endeavor to provide a curly effect.

While the above methods are capable of producing crinkled or curly yarnwhich is suitable for weaving or knitting fabrics with a measure ofelasticity, all of the prior art methods have one or more seriousdisadvantages. A serious disadvantage of all known prior art methods isthat the crinkle or curl is largely developed before the yarn can beemployed for weaving or knitting and this results in yarns which aredifficult to handle. In some instances, the crimp o'r curl produced isof a temporary nature so that it is largely lost as time progresses andthis is particularly true of the crimping action obtained by passingyarns through a crimping Wheel or the like and of the crimping actionobtained by passing the yarn over a dull blade or the like at roomtemperature. In

still other instances, the elasticity of fabrics produced from thecrimped ,o'r curled yarns is not as great as desired, and in otherinstances the prior art processes are inherently expensive due to therelatively complicated equipment needed to practice the processes or dueto the large number of operations which must be performed.

2,919,534 Patented Jan. 5, 1969 It is an object of the invention toprovide metho'ds, for the production of yarns which tend to assume ahighly convoluted configuration, which are not subject to thedisadvantages of prior art processes.

It is another object of this invention to provide a novel method for theproduction of fabrics having a high measure of elasticity which methodpermits the use of yarns having only a slight tendency to assume adistorted configuration and permits the elasticity of the fabric to beprimarily developed subsequent to weaving or knitting.

It is a further object of the invention to provide apparatus, simple inoperation and inexpensive to manufacture, for producing yarns having atendency to assume a highly convoluted configuration. The above, as wellas other objects of the invention, are accomplished by the provision ofmeans for placing ,a running length of thermoplastic yarn under acontrolled tension while it is guided through a sharply angular path,and means for heating the yarn in one portion of the yarn path so thatat least the segment of the yarn transiently disposed at the apex of thesharp angle in the yarn path is at a temperature sufiicient toplasticize but insulficient to melt the yarn. The portion of the yarnpath immediately following the sharply angular portion has a relativelygreat radius of curvature and may be perfectly straight. In this portionof the yarn path, the yarn is preferably allowed to cool under tension.After being allowed to cool under tension, the yarn can be reheatedunder such conditions as to permit it to assume a distortedconfiguration, and this second heating operation fully develops theelastic nature of the yarn. As will subsequently be explained in detail,the second heating operation is most conveniently performed after .theyarn is woven or knitted into fabrics so that a yarn with a minimumamount of curl or crinkle can be employed for the knitting or weavingoperation.

The yarn, subsequent to passage through the angular course but beforethe second heating operation, is hereinafter referred to as latentlyelasticized yarn since, as explained above, it is not until after thesecond heating operation that the yarn develops its full elastic nature.The filaments in the latently elasticizedyarn are characterized by aslightly wavy or coiled appearance when'in an untensioned condition andin most instances have a slightly flattened cross section. The lineardistortions or coils are generally relatively small in number, occurringin some instances as infrequently as 5 .or 6 per inch, and are generallyof a relatively large amplitude, having diameters of from about 1 to 3millimeters in the case of filaments smaller than about 30 denier. Forexample, ina 15 denier monofilament nylon yarn the loops were found tohave an average diameter of 1.85 mm. and in the case of a 70 denier, 34-filament nylon yarn the loops were found to have an average diameter of1.58 millimeters. The loops are generally of random sizes but onoccasion yarn will be found in which all of the loops appear to be of asubstantially constant size. The curls in any instance are usuallytemporarily removed by retaining the yarn under only a slight amount oftension and the lack of liveliness in the latently elasticized yarn is adistinct advantage since in most instances this permits the yarn to behandled by knitting or weaving equipment without many of the precautionswhich are conventionally necessary when handling lively yarns. Where theyarn is composed of a plurality of filaments, the loops in adjacentfilaments will frequently be found to be running in opposite directionsso that the yarn is very bulky in nature.

It is a feature of the invention that if the starting yarn is free oftorsional stresses and if no torsional stresses are deliberatelyintroduced during processing, the .latently elasticized yarn will besubstantially free of torsional stresses and only localized torsionalstresses resulting from loop or coil formation will be present when ineither a tensioned or untensioned condition. The loops or coils areformed such that about 50% of the loops in each filament are in onedirection and the remaining half of the loops are in the oppositedirection so that there is no overall tendency for the yarn to twistwhen the loops are removed by tensioning the yarn. This does not mean,however, that there is a reversal point between each individual loop,but to the contrary the yarn will generally vcarry several adjacentloops running in one direction before a reversal point is encountered,and in some instances the loops will run in the same direction for asmuch as several inches before reversing their direction. Latentlyelasticized yarns according to this invention are, however,characterized by approximately 50% of the loops in each filament runningin one direction and 50% in the other only when the filaments areretained substantially free of torsional stresses, and if the yarn istwisted subsequent to processing or if torsional stresses aredeliberately introduced during processing, the loops will form in amanner to largely relieve these stresses. In other words, by twistingthe yarn during processing, a latently elasticized yarn having the loopsall running in the same direction can readily be prepared. Of course, aswill be apparent to those skilled in the art, the torsional stresses insuch instances are reintroduced when the coils in the yarn are removedunder tension so that a twisted yarn should not be employed wheretorsional stresses are objectionable after weaving or knitting.

The appearance of the yarn in its final form depends upon a number offactors including the conditions under which the second heatingoperation is performed. If the latently elasticized yarn is developed byheating a skein of the yarn in an untensioned condition, the fullyelasticized yarn will be characterized by an appearance approximatingthat of the latently elasticized yarn except that the loops or curlswill be smaller in diameter and more closely spaced. If the yarnfilaments are substantially free of torsional stresses in the firstinstance, the small loops are formed such that about 50% of the loopsare in one direction and the remaining half of the loops are in theopposite direction just as in the latently elasticized yarn. The groupsof coils will be of random lengths and the coils will be of randompitch. If the yarn filaments are tensioned, there will be substantiallyno overall tendency for them to twist, but differential transversestresses will be developed which will cause the filaments, when relaxed,to reassume their coiled configurations. If torsional stresses aredeliberately introduced, it is possible, as in the latently elasticizedyarn, to cause the loops in the fully elasticized yarn to form such thatthey are all running in one direction. The loops, in either instance,will vary in size, but in a well elasticized yarn sample with filamentssmaller than about 30 denier the loops will have an average diameter offrom 0.2 to 0.9 millimeter and will be so closely spaced as to form asubstantially closed helix between reversal points.

The above description of the fully elasticized yarn applies only wherethe second heating operation is conducted before the yarn is Woven orknitted into fabrics, and if the second heating operation is postponeduntil after knitting or weaving, it will be apparent that closed 'loopor coil formations will be inhibited to a large extent. In the case ofknitted fabrics, the yarn will attempt to form into loops and in sodoing will distort the stitches in the fabric to a marked degree so thatthe fabric develops a marked elastic nature and a crepe like appearance.In the case of woven fabrics the second heating operation results in thefabric developing a marked, fine grained, tree bark or pebble effect. Avery interesting tree bark effect can be created by employing latentlyelasticized yarns prepared as above for filling and employingconventional yarn for the warp and such fabrics will also be quiteelastic in one direction.

It is a. feature of the invention that it permits the use of elasticizedyarns and even of elasticized monofilament yarns without plying orsimilar measures in the manufacture of knit fabrics. This has beenpreviously impos sible, because prior art processes are incapable ofproducing a stable, elasticized, monofilament yarn substantially free oftorsional stresses. Knit fabrics formed from nontorsionally stressedyarns according to this invention can be readily distinguished fromfabrics formed from conventional elasticized yarns by the loopconfiguration in the untensioned fabric and by loop behavior uponcontraction of the fabric. If one examines a knit fabric formed fromelasticized yarns made according to this invention without beingtorsionally stressed to a high degree, it will be found, when the fabricis stretched to the maximum of its elasticity, that it has a generallynormal appearance as if it were made from plain yarns, except that theremay be some variation in the size of the interlocking loops of thefabric. When, however, the tension is relaxed and the fabric is allowedto contract in surface area, it will be noticed that a number of thingsoccur. In the first instance, the loops bow and cup so that thepreviously fiat faces of the loops become arcuate and the individualloops no longer lie in a single plane. In a properly finished fabricformed from a well elasticized sample of yarn, the bowing of the loopsis frequently so pronounced that in most instances the previously flatface of the loop or, in other words, the surface generally defined bythe yarn in the periphery of the loop, is bowed through an arc of from60 to Bowing of the loops tends to be especially pronounced near thebase or, in other words, the open part of the loop, but is alsogenerally quite apparent near the top of the loop. Secondly, the looptends to close so that there is a smaller opening at the base of theloop and the yarn forming the loop extends through a greater arc. Insome fabrics a portion of the loops Will close completely, and in mostWell elasticized fabrics the yarn in forming the loop will extendthrough an arc of at least about 270 to 300 when the fabric iscompletely relaxed. A third change noticeable in many instances andparticularly in fabrics knit from monofilament yarns, is that the loopsbecome canted with respect to one another so that they are randomlypositioned with respect to the plane of the fabric. The randompositioning of the loops with respect to the plane of the fabric is aresult of the non-torque elasticization procedure of the invention anddoes not result in a tendency for the courses of the fabric to becomeskewed with respect to the wales thereof. High torque elasticized yarnsmust either be plied or knit double carrier with alternating courses orgroups of courses of S and Z yarn to prevent or minimize skewing.

The mechanism by which the process of the instant invention operates toproduce elasticity in the thermoplastic yarn is not entirely understood,but according to the present understanding of the invention, at leastthree different actions are obtained by passing the yarn through theangular course While in a heated condition. The first action is broadlyanalogous to a phenomenon well known to everyone and which may beobserved by progressively bending a length of ribbon over the blade of aknife or the like to produce a pronounced curl. It is this phenomenonwhich is believed to be, at least to some extent, responsible for thelinear distortions in the yarn which are observed prior to the secondheating operation. This action is apparently not dependent upon the yarnbeing heated as it is passed through the angular course, and, in fact,the action may be noticeably lessened by heating of the yarn as itpasses through the angular course. Likewise this action is not presentlyconsidered to be entirely advantageous since it is desired that thelatently elasticized yarn have as little liveliness as pos sible so thatit may be easily handled during knitting or weaving.

A second phenomenon which can be observed in many instances is adefinite flattening of one side of the fibers andiin some-instances thisflattening occurs to the extent that the yarn fibers actually becomecrescent shaped in cross section. It is not definitely known whetherthis flattening'ofthe fiber has any bearing upon the degree ofelastization but it is not generally considered to be otherwiseadvantageous since in subsequent operations the .fiattened shape of theyarn filaments tends to cause an accumulationof twist asthe yarn ispassed through a guide or the like.

I ..Still;,a :third phenomenon which is observed is the imparting to-theyarn of latent stresses or, in other words,

. stresses that do not make themselves immediately apparent 'bychangingthe linear configuration of the yarn when the tension on the yarn isrelaxed. This phenomenon'is, of course,:quite desirable since it is therelease of "these stresses during the second heating operation, referredto above, that causes the yarn to develop its fullmelastic nature andwhile the exact mechanism involvedin'the'creation of these stresses hasnot been fully determined,;it is known that the stresses are nottorsional innature. For lack .of a better phrase, the stresses arereferred to as differential longitudinal stresses since .their potentialaction is to cause a differential lengthening or shorteningof one crosssectional area of the fiber. While their exact nature is not fullyunderstood, the factors whichcontribute to the creation of thesestresses havebeen accurately determined and will be discussed insubsequent paragraphs.

The yarn to be elasticized according to the new process of thisinventioncan satisfactorily comprise any continuous filamentary strandcomposed of an organic, hydrophobic, thermoplastic fiber material;however, nylon yarns such as those formed from the reaction product ofhexamethylene diamine and adipic acid or from polymers of caprolactam,are preferred since they can be processed with fewer precautions, areoperative through a wider range of conditions and give a higher degreeof elastiz'ation than other types of yarn. The invention can, however,also be employed with polyester yarns, such as those prepared from areaction product of ethylene glycol and terephthalic acid and sold underthe name of Dacron, and under certain conditions, the invention canbeemployed for the elastization of polyacrylic fibers formed by thepolymerization of acrylonitrile or by the co-polymerization ofacrylonitrile with a minor amount of another polymeric monomer. Estersof cellulose, such as'cellulose'triacetate or cellulose diacetate, arealso satisfactory in some instances and a suitable material of this typeis available under the trade name of Arnel. 'Some yarns give difficultynot so much because of their chemical composition or inherent physicalproperties but because of their cross sectional configuration. Forexample, anacrylic fiber soldunder the name of Orlon 'has a crosssectional shape resembling the silhouette of a dumbbell and is verydiflicult to elasticize by the process of this invention. Yarns whereinthe'filaments have a generally circular cross section and a smoothsurface are most readily employed and give the most satisfactoryresults.

The denier and filament size of the yarn to be processed may vary withinwide limits and almost any of the commercially available yarns withinthe previously specified class can be satisfactorily employed. As anillustration of the Wide range of denier and filament sizes which can beemployed, excellent .results have been obtained by employing nylon yarnsof the following descriptions: 15 denier monofilament; l2 denier 4filament; 100 denier 34 filament; 70 denier 34 filament; 200 denier 34filament; 400 denier 68 filament; and '800 denier Sl filament. Undersuitable conditions the denier per filament can range from 1 to 20 andthe total denier can readily be as high as 2,000 or more. For example,excellent results in preparing a nylon yarn for use in the rug industryhave been achieved by processing a filamentary nylon strand having atotal denier of approximately 2,000 in the man: ner previouslydescribed.

Reference will now be made to the accompanying drawings in which Figurel is a schematic view in perspective 'of apparatus suitable forperforming the process of this invention.

Figure 2 is an enlarged view in perspective of a knit fabric accordingto the invention.

Figure 3 is a schematic view in perspective of a second form ofapparatus suitable for performing the process of this invention.

With reference to Figure 1 of the drawings, there is illustrated a pairof yarn supply means 10 and 11 mounted on a suitable frame or supportmember, not illustrated. Yarn ends, indicated by the reference numerals12 and 13, are led from supply packages 1i and 11 through a pair ofguide eyes 14 and 15, about a pair of tension regulating devices 13 and19 and then to a blade assembly generally indicated by the referencenumeral 20. The tension regulating devices 18 and 19 serve the dualpurposes of removing the fluctuations in tension resulting from theremoval of the yarn from the supply packages 10 and 1'1 and of supplyingthe yarn ends to the blade assembly 20 at a proper tension, while theguides 14 and 15 are for the purpose of removing the yarn from the yarnsupply packages 10 and 11 as smoothly as possible. From the bladeassembly 20, which will be subsequently described in greater detail, theyarn ends are drawn through a portion of the yarn path at 21 having arelatively great radius of curvature and are then brought together andpassed through a guide 22 to a pair of driven rolls 23. The two yarnends are then passed through a guide 24 and to a conventional ring andspindle array generally indicated by the reference numeral 25.

The blade assembly, generally indicated by the reference numeral 21 ishere illustrated as comprising an arcuate heater strip 3t), preferablyformed of stainless steel or the like, which has been bent to a radiu ofabout 4 inches in order to present a slightly curved surface to theyarn. The resistance heater strip 30 is adapted to be heated by means ofan electric current passed therethrough and is connected by a pair ofelectrical conductors 31 and 32 to a variable transformer 33 which issupplied with power from any suitable source, not illustrated, throughleads 3 and 35. Mounted on the heater strip 30 by means of a holder 38is a blade member 39 here illustrated as a common razor blade of a typewhich is commercially available under a number of trade names such asSchick, Gem, etc. The actuate edge 40 of the blade extends beyond therear edge of the heater strip 30 a short distance so that the yarn ends12 and 13 pass in contact with the underside of the heater strip andover the edge of blade 39 in an angular path with the edge 40 of blade39 positioned at the apex of the angular path.

in operation, yarn ends 12 and 13 are threaded through the apparatus inthe manner previously described to rolls 2?: and the rolls placed inoperation so that both yarn ends can be passed together through guide 24to the spindle array 25. Before further operation of the rolls 23, theadjustable transformer 33 should be set to give suflicient energy toheater element 30 so that it is heated to the desired temperature. Withthe heater element St at the desired temperature and with the apparatusproperly threaded, the rolls 23 and the spindle array 25 are placed inoperation and thereafter the apparatus requires no further attentionunless an end breaks or a yarn supply becomes depleted. By thisarrangement two single ends are processed to give them a potentiallyelastic nature and are plied together to form a two-ply yarn. It will beunderstood, however, that the yarn ends can be collected singly ifdesired and that conventional apparatus which does not impart a twist tothe yarn can be employed for the collection thereof.

It will be readily apparent to those skilled in the art that apparatusof the type described can readily be constructed by modification of aconventional spinning or twister frame. In either instance all that needbe added is the blade assembly 20, the tension devices 18 and 19 and insome instances the guide member 22. In the case of a twister frame, therolls 23 can constitute the conventional yarn feed means and in the caseof a spinning frame the rolls 23 can constitute the delivery pair of thedrawing rolls. It will also be apparent that a single heater strip ofconsiderable length can serve a multiplicity of blades spaced atselected intervals corresponding to each position of the frame. In suchan arrangement it is usually desirable for the heating element to beinsulated, for example, with foam glass insulation, between the variousblade positions to reduce the heat loss.

In the type of apparatus described, the yarn is forced through an abruptchange of direction by passing the same over an acuate edge and whilethis is presently the most convenient method of accomplishing thedesired result, it will be apparent that the yarn may be caused toundergo the required abrupt change of direction in other ways.

With particular reference to Figure 2 of the drawings, there isillustrated a knit fabric according to this invention formed frommonofilament yarn. For ease of illustration the fabric is shownstretched to an extent short of the maximum although it will beunderstood that the distinguishing characteristics of the fabric aremost pronounced when the fabrics is in a completely untensionedcondition. Canting of the loops with respect to each other and withrespect to the plane of the fabric is illustrated by the loops indicatedby the reference numerals 5i) and 51. This characteristic is among thefirst to disappear upon stretching of the fabric and as illustrated inthe drawings, the loops have been, to a large extent, drawn into theplane of the fabric. The closed nature of the loops is illustrated, forexample at 52, and it will be noticed that a majority of the other loopsare more nearly closed than might be expected in a conventional knitfabric although the loops have, in most instances, been opened to someextent by stretching of the fabric. Bowing of the loops is clearlyevident, for example at 53..

This is presently believed to be perhaps the most im portantcharacteristic, as far as the elasticity of the fabric is concerned, andis generally the last to disappear as the fabric is stretched.

Figure 3 schematically illustrates a second form of apparatus by whichthe yarn of the instant invention can be produced. Numeral 56 denotes aconventional yarn supply package, such as a pirn, bobbin, cake or thelike.

The yarn Y is unwound from this package and passed through a tensiondevice 57, such as a spring-biased disc array. From the tension device,the yarn Y travels upwardly past one side of a blade element 59, overand around the sharpened edge 61 of the blade 59, making an acute bendas it does so, and thence downwardly through a guide 63 to suitabletake-up means, generally designated 65, such as a flanged bobbin 6'7driven by a rotating corkcovered roll 6?.

The blade 59 is wrapped with several turns of electrical heater wire 75to which current is supplied through conductors 73 from a variabletransformer 71 connected to any desired source of electrical power, notshown, by leads 74. Sheets of dielectric material, e.g., mica, areprovided between the blade and heater wire, as at 77.

Heat is supplied to the yarn by convection and radiation as it movespast the side of the blade and by conduction as it moves over the edgeof the blade so that it is in a suitably plastic condition and capableof responding satisfactorily to the action of the blade in the intervalduring which it passes over the edge thereof.

Although the apparatus for producing the novel yarn of this invention isrelatively simple, there are several variables which affect the natureof the yarn produced. For example, the radius of curvature of the bladeedge, the tension in the strand of yarn as it is passed over the 8blade, the temperature of the heater element, the rate of cooling of theyarn after it passes the acuate edge and the linear velocity of the yarncan all affect the nature of the yarn produced and in subsequentparagraphs operative and optimum limits will be set forth for all suchvariables.

The radius of curvature of the acuate edge can vary within reasonablywide limits but is preferably as small as possible without severing theyarn. The smallest possible radius of curvature of the blade in turndepends upon the nature of the yarn being passed over the edge, the sizeof the filaments in the yarn and upon the texture of the material fromwhich the blade is formed. With a blade formed from a finely grainedmaterial, it is possible for the radius of curvature of the edge to beas small as one or two microns when running nylon yarn composed offilaments of about 2 denier or less, but with larger filaments or withother types of yarn, the radius of curvature of the edge shouldgenerally be at least about 3 to 6 microns. Even with nylon yarnscomposed of very small filaments, it is frequently necessary that theradius of curvature be as much as 4 or 5 microns in order forsatisfactory results to be obtained if the blade is formed from a coarsetextured material. A new razor blade generally has a radius of curvatureless than 1 or 2 microns, and it is generally necessary for the edge tobe smoothed very slightly for best results. This can be accomplished byrubbing the blade a few strokes over a finely abrasive material such ascrocus cloth or by polishing the edge with a material such as jewelersrouge.

The maximum radius of curvature of the acuate edge depends primarilyupon the size of the yarn filaments being passed thereover, but willalso vary to some extent with the chemical nature of the yarn beingemployed. However, with any type of yarn, it is a general rule that theradius of curvature should be no more than about 1 to 4 times thediameter of the yarn. For example, when using 70 denier 34 filamentnylon 21 good degree of elastization is generally obtained, only if theradius of curvature of the angular portion of the yarn path is less thanabout 30 microns, but with a yarn having large filaments, such as 15denier monofilament nylon, a blade having an edge with a radius ofcurvature as great as about 7 0 to microns can sometimes be employedwith good results. Even in the latter instance, however, an edge with aradius of curvature less than about 30 microns generally gives thegreatest degree of elastization.

Nylon yarn can be passed over the acuate edge in a dry unlubricatedcondition, but all other yarns generally require the use of alubricating oil for completely satisfactory results, and, even withnylon, better results can be achieved by lubricating the yarn prior toits passage over the acuate edge. In the case of multi-filament nylonyarns, it has been found advantageous to employ a lubricating agentwhich at least partially vaporizes at the temperature of the heaterelement and while the exact reason for this is not known it is believedthat the vaporization of the lubricant results in better heat transferamong the various filaments. In the case of other types of yarn, it isgenerally preferable to employ a lubricating agent which vaporizes onlyto an inappreciable extent at the temperature of the heater strip sincethe yarn needs to be fully lubricated at the time it is passed over theacuate edge or else breakage might occur. In the case of nylon yarns,the preferred lubricating agent has been found to be a low viscositymineral oil such as that sold under the trademark of Esso Mentor 20A. Inthe case of other yarns, the preferred lubricant has been found to beone with a low viscosity and a high flash point and one which can bereadily removed from the treated yarn. Sorbitan trioleate is an exampleof a material which is generally satisfactory. The lubricant can beapplied by means of a felt wick, by means of capillary action or by anyother means generally used in the textile industry for the appli, cationof lubricants to yarns.

; IThexangle of approach and the angle of departure of 'the yarn to theblade may also vary within wide limits, although :the total of these twoangles should be less than about 120 and preferably less than about 100.It is generally advantageous to make the angle of approach relativelylarge, for example from 30 to 100, so that the blade -is displaced fromthe heater element and is, therefore, at a lower temperature. On theother hand, itis generally advantageous that the angle of departure beless than about 50 and preferably as small as the grind of the acuateedge Will permit. When the angle of approach is relatively large, betterthan average results can be achieved by allowing the yarn to follow thesurface of the blade across its entire width after the yarn passes overthe acuate edge. The exact reason or reasons for this are not known withcertainty, but it is known that the yarn should preferably be cooled assoon and as rapidly as possible after its contact with the acuate 'edge,and it is believed that contact across the width of the blade results ina more rapid dissipation of heat from the yarn than is achieved bysimply air cooling the yarn as it travels from the acuate edge.

-If desired, various expedients can be employed to retain the blade at atemperature appreciably below that of the heater element. For example,the blade can be isolated from the heater element by means of heatresistant .insulation or a cooling medium can be circulated in contactwith the blade to retain it at any desired temperature. Whilesatisfactory results have been achieved with the blade at a temperatureequal to that of the heater element, a very marked improvement can 'beachieved by retaining the blade at a temperature of at least about 20'to 50 F. lower than that of the heater element and preferably at atemperature at least about 150 to 250 below the temperature of theheater element.

The tension in the yarn passing over the blade is another importantfactor and this variable must be maintained within specified limits toobtain maximum elasticity. Tension measurements are made on the yarnimmediately after it leaves the blade edge since it has been found thatunder near optimum conditions tension in the yarn before it reaches theheating means is too low to be accurately measured. Operative limits forthe tension in the yarn following its contact wtih the acuate edge varydepending upon a number of factors including the temperature of the yarnand the type of yarn being employed but, as a general rule, theoperative range extends from about .05 gram per denier to approximately1 gram per denier with the preferred range being from about .1 to A gramper denier. The optimum tension will not only vary' with the temperatureof the yarn and the yarn composition but also appears to vary slightlywith yarns of substantially the same composition made by dilferentmanufacturers or even for different lots of yarn made by the samemanufacturer. By carefully controlled tests it has been determined thatthe optimum tension for Du Pont type 200 at a temperature of from about220 to 360 F. at the acuate edge is generally from about 0.15 to 0.28gram per denier.

' The linear velocity of the yarn over the blade may also vary withinwide limits depending upon the temperature of the heater element, thedistance through which the yarn is in contact with the heater element,the distance of the heater element from the edge of the blade and thetype of yarn being passed over the blade. It is important that the yarnvelocity be such that the yarn accumulates suflicient heat to be at theproper temperature at the moment it contacts the acuate edge and it willbe apparent that the yarn velocity required to accomplish this resultwill vary with the above factors. In otherwords, with the yarn incontactwith the heater element for a given distance and with the heater elementat :a fgiven 'temperature, -it will take an appreciably longer period ofcontact for a 70 or 100-denier yam to be heated than will'be requiredfor a 15 or 7 denier yarn, so that a lower yarn velocity must beemployed with the larger yarn. Likewise, if the acuate edge is too farfrom the heater element, there is a tendency for the yarn to coolbetween the heater element and the acuate edge, and it will be apparentthat a smaller yarn will cool more rapidly than a larger yarn so that ahigher linear yarn velocity must be employed in the first instance. Itshould also be mentioned that in some instances the average temperatureof the heater element may be above the melting temperature of the yarn,and in these instances the linear velocity of the yarn must besufiiciently high to prevent the yarn from melting. As a general rule itmay be stated that the operable range for the linear velocity of theyarn over the heater element and acuate edge is from about 1 to 2,000feet per minute or even higher with the preferred range at present beingfrom 200 to 40 0 feet per minute.

Although the distance of the acuate edge from the heater element mayvary within reasonably wide limits and may be as much as two inches ormore, as a gen- .eral rule it is preferred that the acuate edge beplaced as close to the heater element as is possible without actualcontact therewith. By placing the acuate edge as close to the heaterelement as possible, it is only necessary to heat the yarn tosubstantially that temperature at which it is desired that the yarncontact the acuate edge, whereas if the heater element is removed fromthe acuate edge, it is necessary that the yarn be heated sufficientlyabove the temperature at which it is desired that it contact the acuateedge to compensate for the cooling of the yarn that occurs during itspassage from the heater element to the edge. Heating the yarn above theoptimum temperature for contact with the acuate edge is generallyundesirable, since nearly all yarns are weakened to some extent by heatand since temperature control is thereby made more difficult.

The distance over which the yarn is in contact with the heater elementshould, for optimum results, be as great as is possible withoutresulting in an undesirably high tension in the yarn. It will beapparent that the greater the distance that the yarn is in contact withheater element, the greater will be the area of contact and the higherwill be the tension required to transport the yarn, but under someconditions it has been found that the yarn may be maintained in contactwith a heater element for as much as 12 to 20 inches or more withoutintroducing excess tension. A heater element which results in the yarnbeing in contact therewith for a distance of approximately 1 to 10inches is presently preferred in most instances since this length ofcontact is adequate for most small yarns (i.e. below denier) at yarnvelocities below about 400 to 1000 feet per minute. With yarn velocitiesin excess of 400 to 1000 feet per minute or with high denier yarns, itis generally preferable that the yarn be retained in contact with theheater element for a greater distance and under these conditions, aheater element having a width of 10 to 12 inches or more is frequentlyadvantageous. No minimum distance for retaining the yarn in contact withthe heater element can be specified since by employing low yarnvelocities, an almost infinitesimal distance can be satisfactory andgood results have been achieved by employing only the edge of the bladeitself as a heater element. There is, however, generally no advantage inattempting to employ a heater element such that the yarn is retained incontact therewith for less than about inch and as previously stated, ifhigher yarn velocities are to be employed, greater distances of yarncontact should be utilized.

A further factor which need be considered in the production of thelaten-tly elasticized yarn is the temperature of the heater element andit will be appreciated that .the operative range for this variabledepends upon the type of yarn being employed, the linear velocity of theyarn, and the distance for which the yarn is in contact with the heaterelement. If a moderately high yarn velocity is employed, for example 100to 1000 feet per minute, and the contact of the yarn with the heaterstrip is limited to a short distance, for example 1 inch or less, it ispossible to obtain satisfactory results with the heater element at anaverage temperature appreciably higher than the melting point of theyarn. For example, under such conditions operative results can beachieved with nylon yarns with the heater element at a temperature of500 F. or even higher. On the other hand, if the yarn is maintained incontact with the heater element for a relatively long distance, forexample from 3 to 9 inches, it is possible to obtain operative resultswith the heater element at a temperature as low as about 180 F. withnylon yarn. The optimum temperature for the heater element will, ofcourse, depend upon the type of yarn being employed as well as the otherfactors considered above, but even with yarns of the same composition,the optimum temperature of the heater element appears to depend upon thefilament size in the yarn being employed. For example, with the yarn incontact with the heater element for a distance of approximately 3 inchesand with a yarn velocity of 120 feet per minute, an operatingtemperature of from about 320 to' 360 F. has been found to be optimumfor processing 15 denier monofilament nylon (type 66, semidull) while atemperature of from about 330 to 380 F. for the heating element appearsto be optimum when processing 30 denier 10 filament nylon. In otherwords, since the optimum temperature of the heater element will varyslightly depending upon many factors, it is generally advantageous toconduct a series of tests to determine the optimum temperature for theheater element for each particular set of conditions encountered.

The temperature of the heater element has been emphasized since undernormal operating conditions the exact temperaure of the yarn passingover the acuate edge is difiicult to measure, but it will be apparentthat the really important consideration is the temperature of the yarnas it contacts the blade edge. With all yarns of a given constructionand chemical composition there is a Well defined operative temperaturerange for the yarn at this point and some of the values for the heaterelement temperature set forth above are only made necessary or possiblebecause of other variables. Although the exact lower operative limit forany given type of yarn will vary slightly, it can be stated as a generalrule that the lower limit is that temperature which is suificient to atleast largely relax the stresses normally present in the yarn or, inother words, sufficient to relieve the yarn of a large part of theresidual shrinkage present therein. The yarn as it passes over theheating element is generally under such a low tension that it readilycontracts and a temperature which will result in the yarn contracting tothe extent that it has a residual shrinkage of no more than about 1 to5% at the time of its contact with the acuate edge is generallysufiicient to result in operative conditions. For nylon yarns, the loweroperative limit will vary from about 180 F. for type 6, deniermonofilament up to approximately 240 F. for nylon yarns which are verydifficult to elasticize. For other types of yarns the operative lowerlimit will vary from about 190 F. to 300 F. The upper operativetemperature for the yarn as it contacts the acuate edge is generallythat temperature at which the yarn begins to display a tendency to stickto surfaces with which it is in contact, or as it is called in trade andscientific publications, the sticking temperature of the yarn. Theoptimum temperature for the thermoplastic strand as it contacts theacuate edge will vary with a number of factors including filament sizeand chemical composition and generally must be empirically determinedfor each specific yarn. For example, by actual operation it has beenfound that the optimum temperature for Du Pont type 200 nylon, 15 deniermonofilament yarn is about 320 to 340 F., while the optimum temperaturefor type 200 nylon, 70 denier, 34 filament yarn is about 340 to 370 F. A

simple test, which has been found to be of some value in estimating anoptimum temperature for most types of yarn, comprises measuring thetension developed in a given length of the yarn as the temperature israised. As the temperature of the yarn is increased, a point is reachedwhere the tension developed in the yarn falls off rapidly and this pointis generally a near optimum for passing this particular type of yarn tothe acuate edge.

While it is not absolutely necessary that the thermoplastic end of yarnbe cooled after its contact with the acuate edge, cooling the yarn isgenerally more convenient than retainin it at an elevated temperatureand, in most instances, rapidly lowering the temperature of the yarn to200 F. or more results in a better product. As a general rule thetemperature of the yarn should be reduced until it is at least 20 to 80F. below the minimum temperature at which the yarn may satisfactorily bepassed through the acutely angular portion of the yarn path. Forexample, with nylon the temperature of the yarn should be lowered atleast to about F. One convenient method of cooling the yarn comprisessubjecting the yarn, immediately subsequent to its contact with theacuate edge, to the atmosphere so that the yarn end is cooled by aircurrents. Still another and generally more satisfactory method comprisespassing the yarn into contact with a cold metallic surface. Other meansof cooling the yarn end after its contact with the acuate edge willreadily suggest themselves to those skilled in the art.

The radius of curvature of the portion of the yarn path immediatelyfollowing the point where the yarn passes about the acuate edge andwherein the yarn is subjected to cooling conditions, should berelatively large as compared to the radius of curvature of the acuatecurved portion of the yarn path. It is believed that the lack ofliveliness in the latently elasticized yarn is at least partially aresult of passing the yarn from the highly curved portion of the pathinto a portion of the path having a relatively large radius ofcurvature. As a general rule, the radius of curvature of the portion ofthe path immediately following the sharply curved portion should be noless than about 600 microns and should preferably be at least one inch.The length of this portion of the path need not be great and adequatecooling of the yarn can generally be accomplished in A; inch or less,although a length of one inch or more is generally preferred.

To transform the latently elasticized yarn to a fully elasticizedcondition, it is necessary to positionally relax the stresses created inthe yarn as a result of its being passed through the angular path in aheated condition and as previously mentioned, it is an advantage thatthe relaxation of these stresses can be postponed until after the yarnhas been woven or knitted into a fabric. Relaxing the stresses in theyarn after it has been formed into a fabric, however, requires specialprecautions since it is quite difficult to make certain that the yarnsare under a sufficiently low tension that the stresses are, at least toan appreciable degree, positionally relaxed rather than internallyrelaxed or heat-set. In other words, conditions must be such that therelaxation of the latent stresses causes the yarn to assume or attemptto assume a convoluted or irregular linear configuration and if thefabric is rapidly heated, for example, by plunging the same into a hotwater bath, the internal stresses in the yarn will be for the most partinternally relaxed since the bulk of the fabric and the presence ofadjacent courses of yarn will prevent the yarn from assuming thedistorted linear configuration necessary for maximum elasr ticity. Ithas, however, been found that gradually raising the temperature of thefabric favors the positional relaxation of the stresses in preference tothe internal relaxation thereof and for this reason a preferredprocedure comprises gradually raising the temperature of the fabric, forexample, by introducing the same into a cold water bath and thereafterslowly heating the bath to an 13 elevated temperature. It has also beenfound that agitation of the fabric during the heating operation favorspositional relaxation of the internal stresses presumably because theyarns in the fabric, over at least a portion of their length, aregenerally in a near tensionless condition during part of the agitationcycle.

A preferred procedure for developing a high degree of elasticity infabrics woven or knitted from the latently elasticized yarn of thisinvention comprises introducing the fabric into a bath at a temperatureof no more than about 100 F. and preferably at a temperature of no morethan about 80 F. The temperature of the bath is then raised withagitation until the bath has an ultimate temperature of at least about140 F. and preferably above about 180 F. If desired, the bath can beraised to its boiling point, which will be approximately 212 F. Theheating of the bath should be gradual and the rate of temperatureincrease should not exceed about 3 to 4 F. per minute until the bath isat a temperature of about 140 F. and should not exceed about 5 to 6 F.per minute thereafter. The temperature of the bath may be raised at amuch slower rate if desired, and as a general rule the more gradual theheating, the higher the degree of elasticity in the finished product.Agitation of the bath should be initiated before or concurrently withheating and can advantageously be as violent as is possible Withoutinjury to the knitted or woven material. The agitation should beconducted continuously through at least the first stages of the heatingoperation or at least until the bath is at a temperature of about 140 F.and in most instances it is advantageous to continue the agitationthroughout the heating operation and for 5 or more minues after thetemperature of the bath is at the highest value to which it is to beraised.

The particular means for providing the agitation does not appear to beimportant, provided the agitation is sufficiently severe in nature. Thefabric may be mechanically agitated, or it may be subjected to theaction of jets of steam, compressed air or to sonic or supersonicvibrations. In most instances satisfactory agitation can be accomplishedby means of a standard rotary wash wheel machine either of the verticalagitator or horizontal cylinder type, and in the case of small knitarticles, satisfactory results can also be achieved by the use of ahosiery dye machine. The agitation should be such that the fabric isthoroughly flexed at least 2 or 3 times a minute even when thetemperature rise is exceedingly gradual and with a reasonably rapidtemperature rise, i.e. 2 to 5 F. per minute, the fabric should be flexed10 to 20 times or more per minute. For this reason better results aregenerally obtained when using a hosiery dye machine if the speed ofrotation is doubled, for example, increased to 12 r.p.m. for a 25 poundmachine. In the case of small knit articles it is also generallyadvantageous to place the articles loosely in a bag to prevent damageduring the agitated heating operation.

If the full elastic nature of the latently elasticized yarn islto bedeveloped before the yarn is formed into fabrics, agitation and agradual temperature rise are not required since the yarn can readily beplaced in a substantially tensionless condition and when in thiscondition the positional relaxation of the stresses in the yarn prevailsover the internal relaxation of the stresses to the extent that anexcellently elasticized yarn is obtained even if the temperature rise isvery rapid. In this instance, the heating can be conducted byoverfe'eding a single end of the potentially elastic yarn into a heatedfluid or into contact with a heated surface so that the yarn is allowedto coil freely, at the time its temperature is elevated. A hightemperature is not required and satisfactory results can generally beobtained if the yarn is heated to a temperature of only about 120 F.although a temperature of from about 140 to 400 F. is generallypreferred. Care should be exercised to insure that the yarn at the timeit is heated is under as little tension as possible, and

if the tension in the yarn is allowed to rise above about .004 to .01gms./denier, good elasticizing may not be obtained. If the tension inthe yarn is at a proper level, the yarn assumes a highly convolutedlinear configuration almost immediately so that the heating need not becontinued for more than 1 or 2 seconds. As an alternative to the aboveprocedure, the yarn can be formed into skeins and the skeins immersed ina hot liquid or passed through a heated chamber to result in the yarndeveloping its full elastic nature. When the yarn is fully elasticizedby either of these procedures before its formation into fabric, nospecial manipulations of the woven or knitted fabrics are required,although it is generally advantageous to weave or knit the yarn in aloose manner so that upon relaxation of the tension necessary forweaving or knitting, the yarn is free to curl or kink to provide thedesired effect.

Having thus described our invention, what we desire to claim and secureby Letters Patent is:

1. Yarn crimping apparatus comprising, in combination, a source of yarnsupply, a blade having a sharp edge, yarn take-up means spaced from saidblade, guide means to guide an end of yarn, passing from said source ofsupply to said take-up means, in an angular path about said blade withsaid edge positioned at the apex of the angle in the yarn path,tensioning means to place the yarn under tension as it passes about saidedge, and heating means to heat the yarn so that it is at an elevatedtemperature during at least a portion of the time it is in contact withsaid edge.

2. Yarn crimping apparatus comprising a source of yarn supply, a bladehaving a sharpened edge, take-up means spaced from said blade, guidemeans to guide an end of yarn, passing from said source of supply tosaid take-up means, in an acutely angular path about said blade withsaid edge positioned at the apex of the acute angle in the yarn path,tensioning means to place the yarn under tension as it passes about saidedge, and means to heat said blade so that the yarn is heated while incontact with said edge.

3. Apparatus according to claim 2 wherein said blade member is a razorblade.

4. Apparatus according to claim 2 wherein said heating means comprisesan electrical resistance coil circumscribing said blade in contacttherewith.

5. Yarn crimping apparatus comprising a source of yarn supply, a bladehaving a sharp edge, take-up means spaced from said blade, guide meansto guide an end of yarn, passing from said source of supply to saidtake-up means, in an acutely angular path about said blade with saidedge positioned at the apex of the acute angle in the yarn path, tensionregulating means to regulate the tension in the yarn as it passes aboutsaid edge, and yarn heater means spaced from said blade to heat saidyarn so that it is at an elevated temperature at the time it contactssaid edge.

6. Apparatus according to claim 5 wherein said yarn heater comprises anelectrically heated metallic plate having one smooth surface positionedto contact said yarn.

7. Apparatus according to claim 5 including a second source of yarnsupply and guide means to guide an end of yarn from said second yarnsupply about said heater means and said blade edge.

8. Apparatus according to claim 7 including twisting means to twisttogether said two ends of yarn before the same are collected.

9. Yarn crimping apparatus comprising, in combination, a support memberhaving a yarn engaging surface on one face thereof, a blade member,having a sharpened edge, carried by said support member adjacent a sideof said support member generally opposite said yarn engaging surface,said blade member being disposed relative to said support member suchthat said sharp edge extends beyond one boundary edge of the side ofsaid support member adjacent which said blade is supported and such 15that an end of yarn passing about said edge and in contact with saidyarn engaging surface lies in a plane between a point where it is incontact with said yarn engaging surface and a point where it is incontact with said edge, which is at an acute angle to the plane of theface of said blade remote from said support member, and guide means toguide an end of yarn in an acutely angular path about said blade edgewith the yarn in contact with said yarn engaging surface and with saidedge positioned at the apex of the acute angle in the yarn path.

10. A method of crimping a continuous filament thermoplastic yarn whichcomprises continuously passing said yarn in an angular path over thesharp edge of a blade while under tension, said edge being disposed atthe apex of an angle formed between the path of delivery of the yarn tosaid edge and the path of withdrawal of the yarn from said edge,continuously heating the yarn in one segment of the yarn path so that atleast a portion of the length of yarn in contact with said edge is at atemperature suflicient to plasticize but insufficient to melt the yarn,and thereafter collecting the yarn.

11. A method of crimping a continuous filament thermoplastic yarn whichcomprises continuously passing said yarn through a heating zonemaintained at a temperature sufficient to plasticize but insufiicient tomelt the yarn, immediately thereafter passing the heated yarn in anangular path over the sharp edge of a blade while under tension, andcollecting the yarn, said edge being disposed at the apex of an acuteangle formed between the path of delivery to, and the path of withdrawalof the yarn from said edge.

12. A method of crimping a continuous filament thermoplastic yarn whichcomprises continuously passing said yarn in an angular path over thesharpened edge of a blade while under tension, said edge being disposedat the apex of an acute angle formed between the path of delivery of theyarn to said edge and the path of withdrawal of the yarn from said edge,heating said blade so that at least a portion of the length of yarn incontact with the blade edge is raised to a temperature sufiicient toplasticize but insufficient to melt the yarn, and thereafter collectingthe yarn.

13. A method according to claim 12 wherein the tension in the yarnimmediately following its contact with the blade edge is from about0.075 to 0.450 gm. per denier.

14. A method according to claim 13 wherein the radius of curvature ofsaid blade edge is from about to 20 microns.

15. A method according to claim 14 wherein the yarn is nylon and isheated to a temperature of at least about 230 F.

16. A method of crimping a continuous filament thermoplastic yarn whichcomprises continuously passing said yarn into effective relationshipwith a yarn heater to thereby heat said yarn to a temperature sufficientto plasticize but insufiicient to melt the same, passing the thus heatedyarn under tension in an angular path over the sharp edge of a bladespaced from said yarn heater, said edge being disposed at the apex of anacute angle formed between the path of delivery of said yarn to saidedge and the path of withdrawal of said yarn from said edge, andthereafter collecting said yarn.

17. A method according to claim 16 wherein said yarn is subjected tocooling conditions immediately following its contact with said edge.

18. A method according to claim 17 wherein said edge has a mean radiusof curvature of from 1 to 30 microns.

19. A method according to claim 18 wherein said yarn is nylon.

20. A method according to claim 19 wherein said yarn is heated to atemperature of at least 180 F. but below the sticking temperature ofsaid yarn.

21. A nylon yarn, having a substantially permanent tendency to curl whenin a tensionless condition, produced by the method of claim 19.

22. A method according to claim 20 wherein the tension in said yarnimmediately following its contact with said edge is from 0.1 to 0.4 gm.per denier.

23. A method according to claim 16 wherein a second end of continuousfilament yarn is simultaneously passed about said blade edge with saidfirst mentioned end of yarn and said two ends are plied together beforebeing collected.

24. A thermoplastic yarn, having a substantially permanent tendency tocurl when in a tensionless condition, produced by the method of claim10.

25. A knit fabric formed from thermoplastic yarn produced by the methodof claim 10.

26. Yarn curling apparatus comprising a source of yarn supply, a bladehaving a sharpened edge, means for heating the yarn immediately prior toits passage over the sharpened edge, take-up means spaced from saidblade and means adapted to guide the yarn under tension from the yarnsupply, through the heated zone, over the edge of the blade to thetake-up means, so that the path of travel of the yarn defines a V-shapedpath having the blade edge disposed at the apex of such path of travel.

27. A method of crimping a continuous filament thermoplastic yarn whichcomprises continuously passing said yarn in an acutely angular path suchthat at the apex of the acute angle in the yarn path, the yarn isconform d to an arch having a mean radius of curvature of from 1 tomicrons, continuously heating the yarn in one segment of the yarn pathso that at least the segment of yarn transiently disposed at said apexis at a temperature suflicient to plasticize but insuflicient to meltthe yarn, and thereafter collecting the yarn.

28. A method according to claim 27 wherein the temperature of saidsegment of yarn transiently disposed at said apex is at least F. but isbelow the sticking temperature of said yarn, and wherein the tension insaid yarn as it is withdrawn from said acutely angular portion of saidyarn path is from about 0.1 to 0.4 gram per denier.

29. A method according to claim 28 wherein said yarn is nylon.

References Cited in the file of this patent UNITED STATES PATENTS2,166,740 Karplus July 18, 1939 2,199,411 Lewis May 7, 1940 2,211,141Lobasso Aug. 13, 1940 2,392,842 Doell Jan. 15, 1946 2,464,502. Hall eta1 Mar. 15, 1949 2,517,694 Merilon et al. Aug. 8, 1950 2,575,008 DorginNov. 13, 1951 2,601,771 Cameron July 1, 1952 2,668,430 Laros Feb. 6,1954 2,669,001 Keen Feb. 16, 1954 2,702,998 Purcell Mar. 1, 19552,714,812 Leath et al. Aug. 9, 1955 2,730,789 Curry Jan. 17, 19562,736,945 Burleson et al. Mar. 6, 1956 FOREIGN PATENTS 558,297 GreatBritain Nov. 29, 1945

